B 608 
G55 M3 



, HE HARD ROT DISEASE OF GLADIOLUS 

opy 1 



A THESIS 

Presented to the Faculty of the Graduate School 
OF Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



/ 



BY 

LOUIS MELVILLE MASSEY 



Published as Cornell University Agricultural Experiment Station Bulletin 380, 

September 19 16 



THE HARD ROT DISEASE OF GLADIOLUS 



A THESIS 

Presented to the Faculty of the Graduate School 
OF Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

LOUIS MELVILLE MASSEY 



Published as Cornell University Agricultural Experiment Station Bulletin 380, 

September 1916 



t.OM^'^,\(\[(^_^ 



4 



st)*"' ^^'^ 



In cxcUwsff* 
Ccrr.-;11 Univ. I.lbrar* 

FEB Z 19« 



CONTENTS 

PAGE 

The host plant •.••■•; '53 

Economic importance of the gladiokis industry 153 

The disease 1 53 

Economic importance of the disease 155 

Symptoms 156 

On the leaves 156 

On the corms 156 

Etiology 157 

Life history 158 

Pycnidia 158 

Mycelium I59 

Source of leaf infection I59 

Source of corm infection 161 

Longevity of the organism on the foliage and in the soil 162 

Pathogenicity 163 

Inoculation experiments 163 

Pathological histology 167 

Leaf 167 

Corm • 168 

Cultural characters of the fungus 168 

Control ; . . . 172 

Seedling treatments 172 

Corm treatments 1 73 

Healthy corms in soil free from the pathogenes 173 

Healthy corms in soil known to harbor the pathogenes 175 

Diseased corms in soil free from the pathogenes 175 

Spring treatments 1 75 

Autumn treatments ■ • 176 

Experiment i . Treatment of corms with formalin and corrosive 

sublimate solutions 176 

Experiment 2. Formaldehyde gas as a disinfectant 177 

Experiment 3. Hot-water and hot-air treatments of diseased 

corms 177 

Soil treatments 178 

Experiment i . Chemicals 1 78 

Experiment 2. Formalin as a soil disinfectant 179 

Experiment 3. Formalin as a soil disinfectant 180 

Sanitation 1 80 

Bibliography 1 80 



151 



THE HARD ROT DISEAvSE OF GLADIOLUS ' 

L. M. Massey 
THE HOST PLANT 

The gladiolus is a cormous, summer-flowering plant. Pax (1889)^ 
classifies it as a member of the family Iridaceae, of the tribe Ixioideae, 
subtribe Gladioleae, genus Gladiolus. The species of Gladiolus may be 
grown from corms, from cormels (the grayish to black, hard-shelled bodies 
formed on underground stems at the base of the new corm) , or from seed. 
The plants are indigenous to South Africa, where, according to Crawford 
(Crawford and Van Fleet, 1911:3), about fifty species have been dis- 
covered. This writer states: 

It is also a native of middle Africa, central and southern Europe, Persia, Caucasus, 
and the country around the eastern end of the Mediterranean. About forty additional 
species have been found in these localities, and one in Hampshire, England. These have 
been hybridized and crossed until they are so mixed that it is impossible for the ordinary 
grower to say what blood may have entered a given variety — ^nor does it matter. 

ECONOMIC IMPORTANCE OF THE GLADIOLUS INDUSTRY 

According to Hendrickson (191 1), there are from four hundred to five 
hundred acres in the United States devoted to gladioli, the annual pro- 
duction of corms being from 14,000,000 to 15,000,000 and the estimated 
value of- the crops $250,000. In New York State, besides many small 
growers there are two growers each having over one hundred acres devoted 
entirely to the cultivation of gladioli. A list of the members of the 
American Gladiolus vSociety which appeared in 19 14 in the Modern Gladiolus 
Grower (1:31-32) contains two hundred and twenty names, of which but 
sixty-three are those of amateurs and twenty-eight those of foreign dealers 
and growers. The output of these growers and dealers represents only 
a portion of the total output of the United States. Almost every florist 
is more or less interested in the production of corms and flowers of the 
gladiolus, which appears to be increasing in popularity as a cut flower. 

THE DISEASE 

The name hard rot was given to the corm stage of the disease under 
consideration by Wallace (1909:18), who makes no reference to a leaf 
stage. This name was given to distinguish the disease from other corm 

' Also presented to the Faculty of the Graduate School of Cornell University, January, 19 16, as a major 
thesis in partial fulfillment of the requirements for the degree of doctor of philosophy. 

Acknowledgment. The writer wishes to express his indebtedness to Professors Donald Reddick and 
H. H. Whetzel, under whose immediate direction the work was conducted, for helpful criticisms and 
suggestions. 

- Dates in parenthesis refer to bibliography, page 180. 

153 



154 Bulletin 380 

diseases, such as dry rot and soft rot, with which both Wallace and 
Fitzpatrick -^ worked prior to 191 2. The writer took up the investigation 
of these diseases in 191 2 and has given them constant study since that time. 

Apparently the hard rot disease of gladiolus exists wherever gladioli 
are grown. Specimens have been received from many of the largest 
growers in the United States. Horticultural publications contain many 
references to corm rots, and no doubt much of this injury is due to the 
hard rot disease. Plants growing in the greenhouse at Cornell University 
from corms received from Italy by A. C. Hottes bore the leaf stage of the 
disease. The writer has received corms affected with hard rot from 
Canada, Germany, and Holland. 

Prillieux and Delacroix (1894) report having studied a disease of the 
gladiolus in which the tissue was deeply corroded, but the writer is unable 
to determine whether or not it is the same disease as the one considered 
in this bulletin. Unpublished notes placed at the disposal of the writer 
by Professor F. C. Stewart, of the New York- (Geneva) Agricultural 
Experiment Station, mention the only distinction observed, prior to 
Wallace's thesis (1909), between two types of rots. Concerning specimens 
of diseased corms received from a New York State grower, Professor 
Stewart suggested the probability that they were affected with the bac- 
terial disease described by Prillieux and Delacroix, since he was unable 
to locate any trace of fungous hyphae in the diseased tissue. Wallace 
(1909: 15) was of the opinion that the corms received by Professor Stewart 
were affected with the hard rot disease. 

In 1874 Passerini collected specimens of the leaf stage of the hard 
rot disease, which he contributed to exsiccatas of Rabenhorst's Fungi 
Europaei. 

Saccardo (1884) reports the occurrence of the leaf stage of the disease 
on Gladiolus segetum at Parma, Italy, and on Gladiolus gandavensis at 
Coimbra, Portugal. Allescher (1897), in addition to the occiirrence 
on hosts listed by Saccardo, reports the disease as occurring on the leaves 
of Gladiolus palustris in Silesia. So far as known to the writer, the leaf 
stage of this disease has never been reported in America. A "blight" 
is frequently mentioned in horticultural publications, but the descriptions 
of the injury are in all cases so indefinite that it is impossible to determine 
what diseases the writers had under observation. Hicks (1907:35) and 
Childs (1907) write of gladiolus leaf blight, but there is nothing in their 
writings sufficiently definite to make it possible to determine the nature 
of the injury. Halsted (i 894-1 901) reports having worked on gladiolus 
diseases, but leaves the reader in doubt as to what the diseases were. 



3 Unpublished notes of Professor H. M. Fitzpatrick, of Cornell University, covering his investigations 
of gladiolus diseases, were kindly placed at the disposal of the writer. 



The Hard Rot Disease of Gladiolus 155 

Undoubtedly the leaf stage of the hard rot disease occurs more generally 
throughout the country than is indicated by an examination of literature. 
This is due to importation of stock from Europe and exchange of stock 
by growers in this country. On the other hand, the writer has observed 
specimens of the disease on the foliage of plants grown by but three large 
growers. 

Foliage affected with the disease was first observed by the writer in 
1 91 2 in seedling beds, and later on plants grown from cormels. Not 
until the season of 19 15 did the writer find the disease on the foliage of 
large plants, at which time six plants of flowering size were observed to be 
affected. In many cases large flowering plants of different varieties 
have been observed growing in seed beds or among plants from cormels, 
all of which were badly diseased and yet the large plants showed no signs 
of the leaf stage. Large plantations of cormels have been observed in 
which fifty per cent of the plants bore the disease on the foliage. 

Nothing has been found in literature that would indicate that there 
is any relation between the leaf stage and the corm stage of the disease 
under consideration. It has been the writer's fortune to obtain conclusive 
evidence that they are but different stages of the same disease, and the 
experimental data leading to this conclusion are here set forth. 

ECONOMIC importance OF THE DISEASE 

No figures are available to show the economic importance of the hard 
rot disease of the gladiolus, but it must be considerable as compared with 
the extent of the industry. Many thousands of corms are discarded 
during the winter and in the spring at planting time because of their 
diseased condition. During the summer many thousands of corms fail 
to reach maturity, due to the decay of the parent corms in the soil. While 
there are other diseases of the gladiolus, it is the opinion of the writer, 
based on observations made during the past four years, that, a large pro- 
portion of this loss is due to the hard rot disease. Several varieties of 
gladiolus that have been examined showed fifty per cent or more of 
the corms to be affected by hard rot. So far as the writer knows, no 
variety is immune. 

While the loss caused by the leaf stage of the disease is materially less 
than that caused by the corm stage, it is still of considerable importance 
.to the grower. It has been observed that when the foliage of seedlings 
and of plants from cormels is affected by the disease, the corms are smaller 
than those of plantings that were free from disease. Therefore the 
decrease in size must be considered along with the total loss of many 
thousands of corms. To this must be added the extra expense incurred 
by the grower in sorting and selecting more or less healthy corms from 



156 Bulletin 380 

diseased lots, either in filling orders or for his own planting. All in all, 
the loss must take from the producer a yearly toll of surprising magnitude. 

SYMPTOMS 

On the leaves 

The first signs of the disease on the leaf are minute brown or purplish 
brown discolored areas more or less circular in outline. These lesions 
usually appear in July or early August. The color of the diseased areas 
deepens somewhat with age until a shade from reddish brown to almost 
black is reached. Spots of a reddish brown color predominate. In the 
older lesions there is a well-differentiated center, light gray in color and 
dotted with numerous black bodies which are very apparent (Plate xv, i). 
Surrounding the center is a prominent zone, varying from purplish brown 
to black in color, which blends into the green of the healthy tissue. 

The lesions are more or less circular but with straight sides where 
they are limited by the midrib and the edge of the leaf. At first the dis- 
coloration may be visible on only one side of the leaf, but it soon makes its 
appearance on the opposite side, so that lesions appear practically identical 
on either side. They are few or numerous, and vary in size depending 
on conditions. The coalescence of several or many spots may occur, 
causing the formation of a single large necrotic area along the entire 
side of a leaf. Lesions on the tips of the leaves are usually larger and 
less characteristic than those below. In some cases the ashen gray centers 
of diseased areas drop out, giving a shot-hole appearance. This is more 
likely to occur with spots on large flowering plants than with those on 
seedlings. 

On the conns 

Hard rot lesions appear in the fall as minute water-soaked spots, of 
a reddish brown to brownish black color, usually on the sides and the 
lower half of the corm but not infrequently on the upper half as well 
(Plate xvr). It is usually necessary to remove the husks (sheathing leaf 
bases) from the corms in order to see the lesions, although in some cases 
the husk also is diseased. The lesion on the husk serves as an indication 
of the more important lesion underneath. There is no sharp line of 
demarcation between the healthy and the diseased tissue. 

As the spot increases in size, the center becomes sunken, the color 
deepens to a distinct black, and the margin becomes more definite. 
A narrow ring, water-soaked in appearance, still indicates the advancing 
decay. The more definite margin of the older spots is due to the rapidity 
with which the sunken condition follows the advancing water-soaked area, 
due to drying of the tissue. The tissue gradually becomes hard, in 



Bulletin 380 



Plate XV 




P 




P 




HARD ROT LESIONS ON LEAVES AND CORMS 

1, Lesions on leaves of gladiolus seedlings. X 2 

2, Lesions on corms. The two upper corms show lesions well advanced, with 
the diseased area blending into the healthy tissue. At the bottom the corm on 
the left has been cut in two in order to show the depth to which the disease has 
progressed. Natural size 



Bulletin 3S0 



Plate XVI 




HARD ROT LESIONS ON CORMS 
Different stages in the destruction of a corm. X ij 



The Hard Rot Disease of Gladiolus 157 

some cases extremely so, .making it difficult to cut the tissue with a 
sharp knife. 

Many small lesions may coalesce into one large lesion, in some cases 
leaving areas of more or less normal tissue insulated in a large sunken 
area. Enough tissue not completely decayed may be left to indicate 
the margins of the formerly separate lesions. Frequently the disease 
advances so far that the corm is reduced to a hard, shriveled, and wrinkled 
mummy. 

Excepting in very late stages — and in some cases not even then — 
the lesions do not extend deeply into the corm. The usual range is from 
one to five or six millimeters (Plate xv, 2). If conditions are not favor- 
able for the development of the rot, the active border disappears, soon 
assuming the sunken, darkened aspect of the central part. When this 
stage is reached the diseased tissue can be chipped out with the finger 
nail, leaving the apparently healthy tissue beneath, as if the disease were 
not now advancing and the plant had formed a callus over the affected 
area. 

Plants of m^ore or less dwarfed, stunted appearance, which sometimes 
fail to produce blossoms, are to be found throughout the fields during 
the growing season. The leaves of these plants usually turn brown 
and die, the plant having the appearance of having died from drought. 
In a dry season the number of these plants is unusually large. At this 
time there is no decay of the new corm which is being developed, but 
rather the injury is caused by the premature decay of the parent corm 
before the offspring has developed a sufficient root system to enable 
it to supply its own moisture and food. This premature decay of the parent 
corm is not necessarily due to the advancement of the hard rot disease, 
but probably in most cases to the entrance of saprophytes which cause 
a rapid disintegration of the corm. 

ETIOLOGY 

The hard rot disease of the gladiolus is caused by the fungous pathogene 
Septoria Gladioli Passer. Passerini collected specimens of the leaf stage 
of the disease on the foliage of Gladiolus segetum near Parma, Italy, in 
June, 1874, which he contributed to Rabenhorst's Fungi Europaei — 
a collection of exsiccatne material. On this packet of exsiccatas material 
is written the original description of the fungus.^ Passerini noted the 
occurrence of the disease only on the leaves. None of the other investi- 

* Rabenhorst, Fungi Europaei. 
1956. Septoria Gladioli Passer, hb. 
Perithecia punctiformia atra in macula cxarida fulvomarginata: sporae cylindricae subrectae continuae 

hyalinae cirrose cjectae. 
Ad folia G. segetum Vigheffio propc Parmam. 
Junio 1874. leg. G. Passerini. 



iS8 



Bulletin 380 



gators found a sporulating stage of the fungus known to cause the hard 
rot disease of corms, and consequently the septorial fungus on the leaf 
was not associated with the organism causing the rot of the corms. 

Life history 
Pycnidia 

Pycnidia (Plate xv, i) of the hard rot fungus become visible usually 
within four or five days after, or in some cases even simultaneously with, 
the appearance of the lesion on the leaf. They are imbedded in the tissue, 
but protrude sufficiently to form black papillae which are visible to the 
naked eye. 

The pycnidia arise from intercellular mycelium (fig. 38). They 
measure from 100 to 160 /i in diameter by 60 to 130 ju high, the 




Fig. 38. PYCNiDiuM of septoria gladioli 

Section through the pycnidium showing how the spores are borne, 
with a camera lucida.) X Hi 



(Outlined 



average being 127 /x in diameter by 91^1 high. The outer wall of the 
pycniditim consists of pseudoparenchymatous tissue which is brown in 
color. 

From a more or less inconspicuous inner layer of thinner-walled pseudo- 
parenchymatous tissue, hyaline conidiophores arise. From these conidio- 
phores spores are cut off by constriction. In his description of the fungus 
Allescher (1897) describes the spores as being unicellular and measuring 
from 30 to 54 ju long by 2 to 2.5 ,u in diameter. However, an examination 
made by the writer of specimens contained in packet no. 1956 of Raben- 
horst's Fungi Europaei, as well as of fresh material, shows that the spores 
are usually three-septate. As measured by the writer they are from 20 to 
55 iJL long by 2.25 to 4 M in diameter, the average being about 40 by 3 fi. 
The spores from fresh material are cylindrical almost straight, and hyaline. 



The Hard Rot Disease of Gladiolus 



159 



When placed in water containing small pieces of leaf tissue, germination 
occurs in eighteen hours. From one to several germ tubes may develop 
from a single spore (fig. 39). 

Mycelium 

The mycelium in the corm is intercellular (figs. 40 and 41). It usually 
measures from 1.5 to 2.5 ^ in diameter, but is in some cases even double 
this size. The mycelium is septate and varies from olive-brown to 
black in color. 




Fig. 39. SPORES of septoria gladioli 

Some of the spores have germinated. (Outlined with a camera lucida.) X 666 

Source of leaf infection 

No sexual stage of the fungus has been found. Old leaves bearing 
pycnidia when exposed out of doors throughout the winter showed usually 
only empty pycnidia when examined the following spring. From the 
results of experiments subsequently discussed, apparently the mycelium 
of the fungus is able to live over winter in the soil. This suggests the 
possibility that infection is produced on the foliage by rain splashing 
soil containing mycelium on to the plants, or by the plants being beaten 
down on to the soil that harbors the pathogene. However, seedHngs 
around which rye straw was placed to keep them off the ground and to 
prevent soil from being splashed on to them, were attacked by the fungus 



i6o 



Bulletin 380 



as early and as severely as those not so treated ; and attempts to produce 
infection on the foliage of large plants by bending them over on to the 




Fig. 40. HISTOLOGICAL EFFECT OF SEPTORIA GLADIOLI 

Section of gladiolus corm through diseased tissue. The presence of intercellular 
mycelium, and the absence of starch in many cells, should be noted. (Compare 
with figure 41.) X 300 

soil have thus far failed. Not enough work has been done to either prove 
or disprove these suggested sources of infection of the foliage. 




Fig. 41. MYCELIUM OF SEPTORIA GLADIOLI 

The intercellular mycelium is shown much magnified. (Camera lucida drawing.) 

X 600 



In the greenhouse, the incubation period of the fungus on plants 
that were sprayed with water containing spores in suspension was about 
twenty days. 



The Hard Rot Disease of Gladiolus i6i 

Source of conn infection 

An examination of conns harvested from seed beds where the foliage 
was badly diseased, has frequently shown from sixty to seventy per cent 
of them to be affected with hard rot. This, together with the fact that 
infection was produced on corms by placing in contact with them water 
containing spores in suspension (page 167), suggests the probability that 
infection is produced by spores being washed down from pycnidia formed 
on the foliage to the soil, where they germinate and infect the corms. As 
seeds are not planted very deeply, this could readily take place. It is 
unusual, however, for the disease to appear on the foliage of large flowering 
plants; and as pycnidia have not been observed to be formed on the corm, 
it seems that the fungus is ca.rried over the winter primarily, if not entirely, 
in the mycelial stage, no spore form being necessary for the existence of 
the pathogene. 

The fungus can be isolated from lesions on the corms at any time' during 
winter or spring. This shows that the living organism is carried to the 
soil along with the corm at planting time. The offspring from diseased 
corms may or may not be diseased. As discussed under control (page 173), 
selected healthy corms grown in soil in which gladioli have never been 
grown have without exception given sound offspring. This indicates 
that the fungus is not a natural inhabitant of the soil. Furthermore, 
three hundred corms, all of which showed hard rot lesions, were planted 
in soil in which gladioli had never been grown, and seventy-eight per 
cent of the offspring bore hard rot lesions. Thus it seems that, in the 
majority of cases at least, a diseased offspring may be expected from the 
planting of a diseased conn. 

The fungus does not grow directly from the old conn into the new 
one. This has been determined both by observations and by making 
numerous cultures from tissue at the juncture of parent and offspring. 
The fungus must either grow through the sheathing leaf base from the 
old corm to the new one, or else, as is probably the case, grow out into 
the soil, from which it attacks the newly developing corm. 

No observations have been made which would lead the writer to believe 
that all infection does not occur in the field. However, it is conceivable 
that if corms were stored under humid conditions either in contact with 
one another or with moist soil, the fungus might possibly penetrate a 
healthy corm from an infected one or from infected soil ; or, if they were 
stored with soil containing the pathogene around them, there is no doubt 
that, under moist conditions, infection could occur in the storage house 
as well as in the field. 

Diseased corms were minced and placed in soil known to be free from 
the pathogene, in which two hundred healthy corms were growing. The 



i62 Bulletin 380 

pieces of diseased corms were merely sprinkled in among the corms before 
covering them with soil and no attempt was made to see that pieces were 
or were not in actual contact with the healthy corms. Seven per cent 
of the offspring were diseased. 

Longevity of the organism on the foliage and in the soil 

As indicated by the following experiment, the fungus is carried over 
winter on diseased tops: 

Two hundred corms which had been grown for three consecutive years 
in soil that had never before been used for growing gladioli, were again 
planted in similar soil in 191 5. Previous to planting, the corms were 
examined and found to be absolutely healthy. After setting the corms, 
tops from cormels which had been badly affected by the disease the pre- 
vious year and which had remained out of doors on the ground throughout 
the winter, were scattered in the row. The tops and the corms were then 
covered with soil. These plants were harvested in September and the 
corms stored in a cool place. When examined early in December it was 
found that eighty per cent of the corms showed hard rot lesions. Prac- 
tically all the diseased corms had many lesions on them, and the disease 
was well advanced. Septoria Gladioli Passer, was isolated from many 
of these lesions, proving that this fungus caused the disease. Healthy 
corms around which no diseased tops were placed but which were other- 
wise given the same treatment, showed no signs of disease. 

The results of experiments indicate that the fungus is able not only 
to live over winter on old tops on the ground, but also to live in the soil 
throughout a period of at least four years. In 1915 selected healthy 
corms were planted in soil in which gladioli had been grown the previous 
year, and also in soil in which no gladioli had been grown for (a) one 
year, (b) two years, (c) three years, and (d) four years. During the 
intervening time the soil had been planted respectively to (a) rye and a 
crop of rye and vetch, (b) rye and timothy, (c) oats, hay, seeded to clover, 
cover crop of rye and vetch, (d) grass. In each of the five plots of ground 
two hundred and fifty healthy conns were planted, two hundred of them 
being planted in a single row and the remaining fifty in lots of ten at five 
different places in the field. The corms were harvested in September and 
stored in a cool place. 

Results of these experiments were recorded the following December. 
Forty-seven per cent of the corms which were grown in the plot in which 
gladioli had been grown the previous year, were diseased, fifty per cent 
of the diseased corms showing characteristic hard rot lesions. The corms 
from the other plots were diseased as follows: (a) twenty-four per cent, 
forty per cent of which bore hard rot lesions; (b) twenty- three per 



The Hard Rot Disease of Gladiolus 163 

cent, thirty-seven per cent of which bore hard rot lesions; (c) fifty-two 
per cent, eighteen per cent of which bore hard rot lesions; (d) forty-seven 
per cent, ten per cent of which bore hard rot lesions. Care was taken 
during the summer to avoid contaminating these plots by introducing 
affected soil from other fields, and the location was such that it is extremely 
doubtful that the wind could have entered as a factor. Since healthy 
corms planted in soil in which no gladioli have been grown give healthy 
offspring, it follows that the organism must be able to live for at least 
four years without the presence of the living host. No doubt decaying 
parts of plants were left in the soil when the last crop was harvested, 
but it is probable that, at least in the case of plot d, these plant parts 
were entirely decayed in the four years which intervened between the 
harvesting of the last crop of gladioli and the planting of the healthy 
corms used in this experiment. 

Pathogenicity 

The pathogenicity of Septoria Gladioli Passer, was established first 
for the mycelial stage. The mycelium of the fungus was discovere'd by 
Wallace (1909:33), who, after having observed its presence in thin 
sections of diseased tissue of the corm, succeeded in obtaining the organism 
in pure culture. He later (19 10 a) succeeded in producing the character- 
istic lesions on experimentally inoculated corms, and reisolated the fungus. 
Following Wallace, Fitzpatrick (see footnote, page 154) records having 
produced the characteristic lesions on corms artificially inoculated in 
moist chambers, from which the fungus was reisolated. 

Besides noting the constant association of the myceliimi with lesions 
on corms through microscopical examinations of diseased tissue, the writer 
has made numerous isolations of the organism from these diseased areas. 
The growth of the mycelium was studied in pure culture and infection 
was produced at will, not only in moist chambers in sterile sand, but 
also in the greenhouse, and in the field under natural conditions. 

Inoculation experiments 

Corms were selected which after having been in the storehouse for four 
months showed no signs of disease. This necessitated the removal of the 
husks. The surface was sterilized by immersing the corm in fifty-per- 
cent alcohol for three minutes, then in i-iooo corrosive sublimate solution 
for ten minutes, and finally rinsing in sterile water. These corms were 
then planted, some in sterile sand in moist chambers, some in soil in the 
greenhouse in which gladioli had never been grown, and some out of 
doors in soil never before used for the growing of gladioli. 



164 Bulletin 380 

For inoculation, mycelium growing in pure cultures on solid media 
was used. A bit of the mediimi containing mycelium was removed under 
sterile conditions, and in some instances smeared over a part of the unin- 
jured surface of the corm; in other cases the corm was first injured by 
needle punctures and the culture was then smeared on the surface. The 
corms were permitted to remain in the soil for a period of two or three 
weeks, when they were removed and the growth they had made was 
cut off. 

In practically all cases one hundred per cent infection was obtained. 
Most of the corms showed the dark brown, water-soaked areas, char- 
acteristic of the hard rot disease, when dug. The remainder showed the 
lesions very soon afterward. Equally as abundant infection was obtained 
on the uninjured corms as on those punctured by the needle. From 
diseased areas of the affected corms the fungus was reisolated and grown 
in pure culture, where its growth corresponded in every detail with the 
organism used for the inoculation. Corms similarly treated but having 
no mycelium placed in contact with them remained healthy in all instances. 

In order to further test the ability of the fungus to produce disease, 
sound corms were planted in soil in which gladioli had never been grown, 
and permitted to grow to maturity. On August 15, 1914, as the offspring 
were developing from the parent corms, the soil was inoculated with 
mycelium of the fungus. The inoculum was prepared by grinding cul- 
tures of the organism on oatmeal agar with cornmeal, and was applied 
by placing a small handful of the mixture around each corm in immediate 
contact with it. Of the one hundred corms thus inoculated, seventy-three 
showed characteristic hard rot lesions when the results of the experiment 
were recorded the following December. Reisolations of the fungus were 
obtained from many of the diseased corms. Corms from plants which 
had not been inoculated with mycelium remained absolutely healthy. 

The above experiments prove the ability of the mycelial stage of the 
hard rot fungus to attack gladiolus corms. The experiments given below 
show that this mycelium is but a stage of Septoria Gladioli, which Passerini 
described as occurring on the foliage of Gladiolus segetum in Italy. 

A pure culture of the fungus Septoria Gladioli Passer, was obtained 
from the germination of a single spore from a pycnidium formed on the 
leaf of a gladiolus seedling. The resulting fungous growth was identical 
with that obtained from isolations from small pieces of diseased corm 
tissue. Myceliimi thus obtained from a single spore was used to inoculate 
healthy corms, some of which were planted in moist chambers in sterile 
sand, others in soil in the greenhouse known to be free from the pathogene, 
and still others out of doors in soil in which gladioli had never been grown. 
Numerous experiments were performed, and in all cases one hundred 



The Hard Rot Disease of Gladiolus 165 

per cent infection was obtained by smearing a small quantity of an agar 
culture of the mycelium from a single spore on the surface of the corms. 
The fungus was reisolated from diseased areas on the corms, and its 
growth in pure culture was found to be identical with the organism pre- 
viously isolated from corms and from the germination of a single 
pycnospore. 

In order to test the ability of the fungus isolated from a lesion on a 
corm to attack the foliage, a small piece of an agar culture of the organism 
was mixed with a little sterile distilled water and painted on the foliage 
of seedlings and flowering plants growing in the greenhouse. The seed- 
lings were then inclosed in bell glasses lined with moistened filter paper, 
while the parts of the large plants on which the mycelium was placed 
were inclosed in a lamp chimney stoppered at both ends with cotton. 
Seedlings and large plants were similarly treated with mycelium obtained 
from the germination of a single pycnospore. Plants were similarly 
treated, except for the omission of the mycelium, to serv^e as a check. 

Inoculations were successful with both the mycelium from the germinated 
spore and that from the diseased corm. Infection was evident on the seed- 
lings within ten days. The lesions differed somewhat from those found 
under natural conditions, infection manifesting itself in the foiTn of large, 
dark, water-soaked areas, with the early death of the entire area over 
which the inoculum was painted. The lesions produced by mycelium 
from the two dift'erent sources were similar. 

On the large plants, infection was observed within fourteen days after 
inoculation, the lesions being identical on the plants inoculated with 
mycelium^ from the two different sources. At first a dark area, water- 
soaked in appearance, was formed, and then the lesions turned brown 
due to the death of the tissue. The lesions in no case extended much 
farther in area than that covered by the culture of mycelium painted 
on the foliage. The most significant fact is that pycnidia developed in 
these lesions on the leaf on practically all of the twenty-four plants inocu- 
lated with the mycelium, regardless of whether the mycelium was from 
a germinated spore or from a diseased corm. Although many pycnidia 
failed t.o reach maturity, spores were formed in several of them. These 
spores were germinated and the fungus was'obtained in pure culture. 

In October, 1914, Septoria-like spores were found in a culttue of the 
organism isolated from a diseased corm. These spores, together with 
others obtained from pycnidia on seedling leaves, were used in the 
following experiments : 

Seeds were planted in three flats in the greenhouse and the plants were 
permitted to grow until they were from two to four inches high. The 
plants in one flat were sprayed with water containing, in suspension. 



1 66 Bulletin 380 

spores from a culture of the fungus isolated from a diseased corm; the 
plants in the second flat were sprayed with a suspension of spores from 
pycnidia formed naturally on seedlings; the plants in the remaining flat 
were sprayed with water containing no spores, for a check. The seed- 
lings were then covered with bell glasses lined with moistened filter 
paper, and the three flats were placed in a large moist propagating 
chamber for seventy-two hours. 

An examination of these seedlings twenty days after they had been 
sprayed with the suspension of spores in water showed evidence of infec- 
tion. Small yellowish brown areas were apparent and numerous pycnidia 
appeared in these lesions a few days later. The lesions were characteristic 
of those found on the seedlings under natural conditions. The check 
plants alone remained healthy, infection occurring on plants which were 
inoculated either with spores from culture or with spores from pycnidia 
formed under natural conditions. The fungus was again obtained in 
pure culture from the germination of single spores from pycnidia formed 
on both lots of infected plants. 

It then seemed desirable to determine whether or not corms could 
become infected by spraying spores upon them. The surfaces of thirty 
healthy corms -were sterilized by iinmersing them first in fifty-per-cent 
alcohol for three minutes, then in i-iooo corrosive sublimate solution 
for ten minutes, and finally rinsing in sterile water. Ten of these corms 
were then planted in each of three moist chambers containing moist sand 
which had previously been subjected to steam at ten pounds pressure 
for two hours. Corms that were particularly depressed at the crown 
were selected for the experiment, in order that a cubic centimeter or 
more of water could be held in each of these cavities. Water containing 
spores in suspension was placed in the depressed areas of the corms in 
two of the moist chambers. The spores for one chamber were obtained 
from pycnidia formed natural!}' on the foliage of seedHngs, while for 
the other chamber the spores were obtained from a culture of the fungus 
isolated from a diseased corm. The third chamber was used for a check, 
water containing no spores being placed in the cavities of the corms. 
One-half of the corms in each chamber were then pricked with a sterile 
needle in the area covered by the water. 

Observations made twenty days later showed most of the corms in 
the two chambers which were inoculated with spores to be infected. Six 
days later, when they were removed, all the inoculated corms showed the 
characteristic hard rot lesions, while the check corms remained healthy. 
Lesions were as abundant on corms that had not been injured as on those- 
punctured with the needle. About one-half of the corms showed hard rot 
lesions on the sides, where evidently spores had been washed over from 



The Hard Rot Disease of Gladiolus 167 

the concave crowns. The fvmgus was isolated from many of these diseased 
areas and again obtained in pure culture. 

In the spring of 19 15 healthy corms were planted in soil in which gladioli 
had never been grown, and allowed to grow to maturity. On August 21 
the soil was removed from around thirty of these plants and water con- 
taining a suspension of spores was poured around the corms. At this 
time the offspring were about one-half inch in diameter. The spores 
for inoculating fifteen of the corms were obtained from pycnidia formed 
naturally on the foliage of seedlings, while for the other fifteen corms 
the spores were obtained from a culture of the fungus isolated from a 
diseased corm. For a check, corms were given the same treatment 
except that the water poured around them contained no spores. The 
soil in which these plants were growing was kept moist for the follow- 
ing three days. 

The corms were harvested in the following September and stored in a cool 
place. When examined in November it was found that ten of the fifteen 
corms inoculated with spores from pycnidia showed hard rot lesions; 
also, six of the fifteen corms inoculated with spores from culture showed 
lesions characteristic of the hard rot disease. The check plants remained 
healthy. This experiment is significant in showing not only that spores 
from cultures and from naturally formed pycnidia are able to infect the 
corms, but also that it is possible for infection to occur on the corms from 
spores discharged from 
pycnidia on the leaves. 
The spores are washed 
down into the soil, 
where they germinate 
and produce infection. 

Pathological histology 

Leaf 

An examination of 
thin sections of leaves 

•u • J- „ J Fig. 42. HISTOLOGICAL EFFECT OF SEPTORIA GLADIOLI 

bearing young diseased ^ ^, .,,.,,, , . , , , , 

. Camera lucida drawing of a free-hand section through a hard rot lesion 

areas shows the lesion on the leaf of a seedling. The cells are beginning to shrivel and collapse. 

produced by the fun- 
gus to be necrotic. The cells turn brown, shrivel, and collapse (fig. 42). 
Here and there a cell may be found filled with a yellow, granular or 
oil-like substance the identity of which is undetermined. The diseased 
area is usually but from one-third to one-half the thickness of the 
healthy tissue. 




1 68 



Bulletin 380 



Corm 

In order to study the histological changes that occur in the corm, com- 
parative studies of healthy and diseased tissues have been made. Both 
microtome and free-hand sections have been used, the former being less 
satisfactory because of the difficulty encountered in sectioning prepared 
material. Sections were stained with a weak solution of iodine in order 
to study starch content of cells, and with Haidenheim's iron-alum-haema- 
toxylin and aniline blue for a general study of the tissue. 

While the cells of healthy tissue are densely packed with starch, those 
of diseased tissue show but very few starch grains or none at all (figs. 40 
and 41 [page 160], and "43). This, together with the deposit in the 
diseased area of a yellow substance of undetermined composition, is the 

most pronounced effect to 
be noticed by comparing 
sections of diseased and 
healthy tissue. Espe- 
cially in the early stages 
of the disease, nuclei and 
even the cytoplasm 
appear but slightly dis- 
turbed. The cell walls 
retain their shape for 
some time after the starch 
has disappeared. Later, 
shrinkage takes place and 
the cells collapse, the 




Fig. 43. HISTOLOGICAL EFFECT OF SEPTORIA GLADIOLI 



Camera lucida drawing of a microtome section through medium 
of healthy and diseased tissue. The layer of comparatively thin- 
Walled cork cambial cells separating the starch-filled healthy cells 1,1 • ■,• 1 
from the diseased cells, which contain little or no starch, should WallS beCOmillg dlStOrtcd 

and broken. This last 
effect is no doubt due to loss of moisture rather than to any direct 
action of the fungus. 

A layer of cork cambium is formed at the juncture of the diseased 
and the healthy tissue (fig. 43). Young, actively advancing lesions do 
not show this layer of thin-walled cells, but it is to be found in those 
instances in which it appears that the advance of the disease has been 
checked and the canker healed. In cases in which the diseased area 
can be chipped out, the break is at this layer of cork cells. 

Cultural characters of the fungus 

Pure cultures of Septoria Gladioli Passer, were obtained from isolation 
plantings of diseased tissue from a corm. The surfaces of corms showing 
hard rot lesions were disinfected by immersing them in fifty-per-cent 
alcohol for three minutes, then in i-iooo corrosive sublimate solution 



The Hard Rot Disease of Gladiolus 



i6g 



for ten minutes, and finally rinsing in sterile water. By means of a sterile 
scalpel the surface of the corm was cut away and a small piece of the 
tissue at the advancing margin of the lesion was removed to a sterile 
medium. Comparatively few contaminations were obtained in the large 
number of isolations made in this manner. 

No marked difference was observed in the growth of the mycelium 
on nutrient or on soil-extract agar, or on other solid media consisting of 
agar and various plant decoctions, such as of gladiolus, potato, oats, com, 
and beans. On the 
other hand, rolled-oat 
agar^ proved slightly 
more favorable for 
mycelial growth, and 
spores were produced 
by the fungus only 
when growing on this 
medium. For this 
reason rolled-oat 
agar was used almost 
entirely for culturing 
the organism during 
the last year of study, 
and the following cul- 
tural characters of 
the fungus are a rec- 
ord of its growth on 
this mediimi. 

Macroscopically, 
no growth from bits 
of diseased tissue 




Fig. 44. MYCELIUM OF SEPTORIA GLADIOLI 

Camera lucida drawing of mycelium of the hard rot fungus growing 

placed m medium m '-'^ rolled-oat agar. A, colorless strands of hyphse radiating from a bit 

_ of diseased tissue. B and D, cell walls that have thickened, the cells 

previouslv poured having assumed a globose form. C, colorless hyphas to be found in old 

■^ ... . cultures. E, an intermediate stage between A and B. X 600 

petri dishes is evident 

for from seven to fourteen days. However, if the plate is examined under 
the low power of the microscope, mycelium radiating from the transferred 
piece of tissue can be seen in about four or five days from the time of 
making the culture. Frequently the first macroscopical evidence of growth 
is the appearance of a black growth on the transferred piece of tissue, 
which may be completely covered before the organism invades the 



5The rolled-oat agar was prepared as follows: 50 grams of rolled oats, in 700 cubic centimeters of dis- 
tilled water, was cooked in a double boiler for about an hour, or until the oats were thoroughly cooked 
through. Most of the solid matter was then squeezed tlirough cheesecloth. To this was added 15 grams 
of agar and enough water to make one liter of medium. 



170 Bulletin 380 

medium. Soon a dense, black colony spreads very slowly into the sur- 
rounding medium. After growth of a month the colonies usually do not 
exceed one or two centimeters in diameter. If portions of a colony are 
transferred to flasks of media or to other plates, the resulting growth is 
somewhat more rapid. 

Some of the characters of the mycelium as grown in culture are shown 
in figure 44. The first strands of hyphae to be seen radiating from the 
piece of diseased tissue are hyaline (fig. 44, a). Color frequently makes 
its appearance in streaks, which radiate from the piece of diseased corm, 
where the hyphae seem to become gnarled. Cells of the much-septate 
mycelium thicken, assiiming a globose form (fig. 44, b). Well-defined 
globular bodies, which appear to be oil drops, soon appear within the 
cells. Osmic acid causes these to turn brown. The walls turn brown 
with the appearance of these bodies, giving the colony its black color 
when viewed macroscopically. The globose or subglobose cells of the 
hyphas may remain attached, forming chains, or may separate into 
individual cells (fig. 44, b). 

Although the growth is usually confined beneath the surface of the 
medium, small scant patches of white, aerial mycelium are found occa- 
sionally. The hyphas of old cultures is of two kinds: one of compara- 
tively long, colorless cells measuring from 1.5 to about 4. fj. in diameter 
(fig. 44, c, e) ; and one of short, thick, globose cells containing the oil 
drops mentioned above, measuring from 3 to 6 or 7 ^i, or sometimes even 
12 ju, in diameter (fig. 44, b, d). 

Scattered through the colonies are areas which under the microscope 
appear denser and blacker than other areas. These seem to be caused 
by a gnarling, or balling, of the hyphae at these points, together with 
the anastomosing of cells of different hyphae, as if pycnidia or other 
fruit bodies were to be formed. Cultures have been examined inter- 
mittently throughout a period of over three years, and no further develop- 
ment of these masses of hyph« has been observed. 

Spores of Septoria Gladioli Passer, were first observed in culture in 
October, 19 14. The mycelium on which these spores were formed was 
isolated in the preceding June, from a hard rot lesion on a corm. This 
mycelium was allowed to grow in a tube of rolled-oat agar from June 
until August 20, when a square block of the medium containing mycelium 
was transferred to the slanted surface of about 200 centimeters of rolled- 
oat agar contained in a 300-cubic-centimeter Erlenmeyer fiask. The 
medium contained in this flask was freshly prepared. There were about 
10 cubic centimeters of water of condensation in the flask at the base of 
the slanted medium. The culture from which the transfer was made was 
well dried at the time when the square of medium containing myceliiim 



The Hard Rot Disease of Gladiolus 171 

was removed, and this condition may have influenced spore formation 
when the mycelium was placed on the freshly prepared medium. 

By approximating the above conditions the writer has been able to 
bring about the formation of spores in cultures of the myceliimi from 
other sources than the one above noted. Spores were formed in a culture 
of the mycelium obtained from the germination of a single pycnospore 
formed naturally on the leaf. Spores formed in cultures of mycelium 
isolated from corms and from germinated pycnospores were identical 
in shape and size, thus materially helping to establish the identity of 
the two previously unconnected organisms. 

Spores in culture have always appeared as minute pinkish white pustules 
on the upper edge of the block of medium containing mycelium trans- 
ferred from the old culture. Later these pustules may appear scattered 
over the surface of the medium of the flask to which the transfer was 
made. If at this time transfers are made from this flask to another, the 
pustules are formed more readily and in greater abundance. 

Owing to difficulties encountered in obtaining sections or mounts of 
these pinkish white elevations, but little is known of their structure, 
especially in reference to the formation of the spores. Normal pycnidia 
such as those formed on the foliage are not produced. The spores are 
formed in a very loose stromatic mass. There is an abundance of dense, 
pinkish white mycelium, which is still in evidence after spores are no 
longer to be found associated with the pustules. 

Spores formed in culture are variable in size, ranging from 25 to 97 ^i 
by 1.8 to 3.7s M. the average being 58 by 2.71 /x. Dilution plates of these 
spores were made in nutrient agar and practically one hundred per cent 
germination was obtained within a period of eighteen hours. The result- 
ing mycelial growth was not so brown in color as that isolated from corms. 
Many minute, black dots appeared, which, when examined under the 
microscope, proved to be aggregations of short, thick-walled cells formed 
commonly and more abundantly in cultures of the fungus isolated from 
corms. Transfers were made from these plates to tubes of rolled-oat 
agar, where the resulting growth was identical with that obtained by 
isolations made from diseased corms. 

In order to correlate the growth of mycelium isolated from diseased 
tissue of corms with that isolated from the leaf, dilution plates of spores 
from naturally formed pycnidia were made. From these dilution plates 
individual spores, which were so located that they could be removed 
singly, were transferred to other plates where germination was observed 
under the microscope. The resulting mycelial growth in all cases has 
been identical with that isolated from corms when the two were growing 
under similar conditions. 



172 Bulletin 380 

CONTROL 

The great need of some method of combating the organisms causing 
rots of gladiolus corms was early impressed upon -the writer, and many 
suggested methods of general application were tried for the control of 
the rots collectively rather than separately. Another disease, designated 
by Wallace (1909:61) as dry rot, was found to be present along with 
the hard rot disease in stock which was used in all control experiments. 
The lesions produced by the fungi causing these two diseases are so similar 
that they can be distinguished only in the earliest stages, and not even 
then with a great degree of accuracy. Cultural isolations of the organisms 
will often show a lesion to have been caused by the hard rot fungus when 
it was selected as being a dry rot lesion, or vice versa. Not only are the 
lesions produced by the two fungi similar, but the life histories of the 
organisms are not materially unlike except for the fact that no spore 
form of the dry rot fungus has been found. From all indications, a treat- 
ment applicable to the control of one disease should be of value in con- 
trolling the other. At least fifty per cent of the conns used for experimental 
purposes were affected with the hard rot disease. This estimate is based 
on observations and cultural studies throughout a period of several years. 
In practically all cases, after the corms were treated, the organisms have 
been isolated from diseased areas in order to make it absolutely certain that 
both were present, and in no case has any treatment resulted, so far as 
the writer was able to judge, in materially changing the ratio of the corms 
affected by the two diseases. 

In view of the fact that control experiments were conducted previous 
to, and simultaneously with, life history studies, it is not surprising that 
some treatments which at first seemed worthy of trial failed to bring 
results. Many of the following treatments have given negative results. 
This does not wholly deprive them of their value, for they serve to narrow 
down the field of experimental possibilities of control. Many data have 
been obtained from the treatments which will be valuable in a further 
study of control measures. 

SEEDLING TREATMENTS 

The hard rot disease on the foliage of seedlings has been materially 
reduced by spraying with bordeaux mixture used at the strength of five 
pounds of copper sulfate and five pounds of lime to fifty gallons of water. 
In 1 91 4 the first spray was applied on July 17. This application was 
followed by eight other treatments made at intervals of about seven days. 
Because of the smooth surface of the foliage, it was necessary to use a 
"sticker," or adhesive, to cause the fungicide to adhere to the plants. 
The " sticker " used consisted of resin two pounds, sal soda (crystals) 



The Hard Rot Disease of Gladiolus 173 

one pound, and water one gallon, which, after being boiled until a clear 
brown color was obtained, was added to each fifty gallons of the bordeaux 
solution. The seedling beds were sprayed twice the same day for each 
application, the second spray being applied as soon as the first was dried 
on the foliage. This was done in order to thoroughly cover the plants. 
A hand sprayer was used, in which a pressure of from three and one-half 
to five pounds could be maintained at all times. 

H. H. Groff, of Simcoe, Ontario, informed the writer that he was 
successful in controlling a disease of the foliage of seedlings by spraying 
with a solution of copper sulfate in water. Specimens of the disease sent 
by Mr. Groff to the writer proved to be the hard rot disease. From the 
nature of the foliage of the gladiolus, it is probable that the plant is more 
resistant to spray injury than are most plants and that a solution of copper 
sulfate could be used without causing injury. However, no experiments 
have been conducted by the writer using copper sulfate solution as a spray 
for the control of this disease, and it is very unlikely that results could be 
obtained, because the copper sulfate would be washed away with the 
first rain. 

Although spraying will greatly reduce the amount of disease on the 
foliage, a simpler and more efficient method is to plant the seed in soil in 
which gladioli have never been grown. When this was done, and care 
was taken not to carry parts of diseased plants or soil bearing the fungus 
to these seedlings, it was found that not a single diseased plant appeared 
during the summer. The corms of these plants were materially larger when 
harvested than the corms of plants whose foliage was attacked by the 
hard rot fungus, and no evidences of disease on the corms were observed. 
This is the logical way to control the hard rot disease, which causes so much 
damage in seedling beds. It is doubtful whether any grower plants 
such a large quantity of seed, or has such a limited area of ground, that 
soil in which gladioli have never been grown cannot be obtained for this 
purpose. If this plot is kept isolated and care is taken not to introduce 
the pathogene into the soil, there appears to be no reason why seedlings 
cannot be grown on the same area year after year, if necessary, at least 
so far as the hard rot disease is concerned. 

CORM TREATMENTS 

Healthy corms in soil free from the pathogenes 

Selected healthy corms have been grown for the past four years in 
soil in which no gladioli had ever before been planted, without a single 
corm's becoming diseased. The fact that these corms were stored through- 
out each winter in a room containing diseased corms leads to the con- 



174 Bulletin 380 

elusion that the fungi eausing the hard rot and dry rot diseases are not 
disseminated in storage. It is obvious that in order to obtain results from 
the selection of healthy corms, rigid and painstaking care must be exercised 
to select corms known to be absolutely free from disease. Any doubtfully 
healthy corms must be rejected, for a single diseased corm may serve to 
infect the soil in which healthy corms are planted. 

To select healthy corms it is necessary to remove the husks and to be 
sure there is no evidence of disease on the corms. It is best to do the 
selecting in the spring, as near planting time as possible, for, whereas 
a corm may be infected in the fall at digging time and still show no evidence 
of being diseased, the lesion is sure to be noticeable by planting time. 
Previously to planting these corms it is advisable to treat them with 
a five-per-cent solution of formalin for thirty minutes, in order to kill 
any parts of the pathogenes which may be clinging to them. 

In 1 9 1 2 from two thousand to three thousand healthy corms were selected 
in the manner suggested above. They were planted each year in soil 
that had not been under cultivation for about twenty years. A com- 
mercial phosphate fertilizer was applied to the experimental plots at the 
rate of about five hundred pounds to the acre, and the corms were planted 
in the usual manner. Care was exercised to see that no foreign soil nor 
diseased plant ]3arts were introduced into these plots. The plants received 
the usual amount of cultivation and were subjected to the same con- 
ditions as commercially grown plants. Spikes of flowers were cut during 
the blooming season, and the corms were harvested and stored each 
autumn in the ordinary way. 

This process of selecting healthy corms and growing them in soil free 
of the pathogenes is the only means known that will give an absolutely 
healthy crop. Of course the large amount of labor, the carelessness of 
laborers, the need of a larger outlay of land, and the inability to procure 
land on which gladioli have never been grown or at least not for many 
years, are some of the important factors that will at once suggest themselves 
to growers, especially the larger growers who produce many thousands 
of corms annually. It is admitted that this is a slow and somewhat 
undesirable method from many standpoints, yet it is a process that has 
proved conducive to results, and undoubtedly can find some application 
by all growers. Small growers can readily and with no great loss adopt 
such a method for growing gladioli. Larger growers can adopt the process 
in part. 

Such a method could be begun on a small scale, by selecting as many 
healthy corms the first year as conveniently possible and planting them 
in soil in which gladioli had never been grown. More selected corms 
could be added to this lot the second year, and so on until the grower 



The Hard Rot Disease of Gladiolus 175 

gradually worked away from diseased to healthy stock. The opportunity 
for healthy corms to become diseased is thus lessened, and diseased con- 
ditions are in general improved. 

Healthy corms in soil known to harbor the pathogenes 

When selected healthy corms were planted in soil in which gladioli 
had been grown the previous year, the offspring were diseased. The 
amount of disease varied from twenty- three to forty-seven per cent. 
The possibility suggested itself that some treatment might be devised 
which would protect the offspring of the sound corms that were planted, 
from the pathogenes that must be in the soil. 

An experiment was conducted in 19 14 in which the corms of the various 
plots were treated with different chemicals. A small handful of the 
chemicals was placed over each corm previously to covering the corms 
with soil. The chemicals used were: plot i, sulfur; plot 2, air-slaked 
lime; plot 3, acid phosphate; plot 4, soot. The soot was suggested by 
a grower who claimed to have obtained good results through a liberal 
application of this substance to the soil. The plants received ordinary 
cultivation during the summer, and the offspring were harvested and stored 
in the usual manner. In December, when the results of the experiments 
were recorded, it was found that none of the treatments were of any value, 
the percentages of disease in the treated plots being practically the same 
as that in a check plot where no treatment was given. The experiment 
was repeated in 191 5 with the same results. 

Diseased corms in soil free from the pathogenes 

Spring treatments 

When diseased corms that had received no treatment were planted in 
soil free from the pathogenes, it was found that the offspring gave various 
percentages of disease. Seventy-eight per cent of the offspring from 
three hundred corms bearing typical hard rot lesions, which were planted 
in soil free from the pathogenes, were diseased. In other instances, thirty- 
three and fifty-seven per cent diseased offspring, respectively, were recorded 
from the planting of two lots of three hundred corms affected with either 
hard rot or dry rot, or both. 

An experiment was conducted in 19 14 to determine whether or not 
some treatment could be given these corms at planting time which would 
lessen the amount of disease in the offspring when the corms were grown 
in soil free from the pathogenes. Corms that bore typical hard rot lesions, 
and others that were affected with either the hard or the dr}^ rot disease 
or both, received the following treatments: (i) formalin at the rate of 



176 Bulletin 380 

one pint of commercial formalin to fifteen gallons of water, for eighteen 
hours; (2) corrosive sublimate, i-iooo solution, for eighteen hours; 
(3) chemicals, in which the corms were rolled and with which they were 
covered after being placed in the rows and before covering them with 
soil. The chemicals used were sulfur, air-slaked lime, acid phosphate, 
and soot. The corms were planted in soil in which gladioli had never 
before been grown, and received ordinary cultivation during the summer. 
When the corms were examined in December, 19 14, the results obtained 
indicated that none of the treatments were effective in reducing the 
amount of disease. The experiment was repeated in 191 5, with the 
same results except that corms over which a handful of sulfur was placed 
were injured severely by the chemical. Such treatments of diseased 
corms have proved to be of no value in controlling the hard rot and dry 
rot diseases. 

Autumn treatments 

vSince the lesions on corms attacked by the hard rot and dry rot organisms 
are materially smaller in the autimin when the corms are dug than in the 
winter, it was thought that possibly the corms could be given some treat- 
ment at digging time whereby the pathogenes within the tissues would 
be killed. Consequently the following experiments were performed 
with the hope of at least lessening the extent of injury to. the corms. 

Experiment i. Treatment of corms with formalin and corrosive sublimate 
solutions. — In 19 14 one thousand corms, of which many had lesions 
in various stages of advancement at digging time, were treated, 
immediately after digging, with formalin at the strength of one pint of 
commercial formalin to fifteen gallons of water, in which they were left 
for eighteen hours. An equal number of corms were treated with i-iooo 
corrosive sublimate solution for eighteen hours, and an equal number 
were left untreated for a check. After treatment the corms were cured 
out of doors and then stored as usual. 

In the following December, when the results of these treatments were 
recorded, it was found that neither had reduced the arnount or the extent 
of the diseases. Thirty-five per cent of the offspring from the untreated 
corms were diseased, while thirty-seven and thirty-eight per cent, 
respectively, of the offspring from the corms treated with formalin and 
corrosive sublimate solution were diseased. 

The same experiment had been performed the previous season (1913), 
with the result that about ninety per cent of the corms of both the treated 
lots were diseased while the corms in the check were but seventy per- 
cent diseased. This remarkable situation is difficult to explain. There 
was a prolonged period of wet weather about the time the treatments 



The Hard Rot Disease of Gladiolus 177 

were made, so that the corms remained wet for about a week after they 
were treated. The corms were either injured by being subjected to the 
action of the reagents for so long a time, or else the increased per- 
centage of diseased corms was due to some other abnormal condition 
brought about by the wet condition of the corms. Many of the corms 
bore lesions which were not characteristic of either the hard rot or the dry 
rot disease, from which neither the dry rot organism nor Septoria Gladioli 
Passer, could be isolated. 

Experiment 2. Formaldehyde gas as a disinfectant. — On the basis of 
successful experiments performed for the control of potato scab by the 
use of formaldehyde gas, diseased corms were subjected in 19 13 to a 
similar treatment. Obviously this would eliminate the himiid condition 
arising from the use of solutions. 

In this experiment the gas was generated by the potassium permanganate 
method. At harvesting time one thousand corms were placed, immediately 
after digging, in shallow trays in a large air- tight box. The formaldehyde 
gas was obtained by using enough potassium permanganate to generate 
gas at the rate of three pints of formalin and twenty-three ounces of 
permanganate crystals to five hundred cubic feet of space, it having 
been previously determined that corms thus treated were unharmed. 
The treatment extended over a period of twenty-four hours. The corms 
were then thoroughly cured in the open air and stored as usual. 

In January, 19 14, when the results of this treatment were recorded, 
it was found that sixty-nine per cent of the corms were diseased while 
seventy per cent of the untreated corms from the same lot were diseased. 
The hard rot and dry rot organisms were isolated from many lesions, 
showing both organisms to be alive. The difference of one per cent in the 
amount of disease can easily be explained on the basis of experimental 
error, with the resulting conclusion that formaldehyde gas as used in 
this experiment is of no value in controlling the corm rots of gladioli. 

Experiment j. Hot-water and hot-air treatments of diseased corms. — In a 
third experiment some means was sought whereby diseased corms could 
be subjected to heat, which would kill the organisms within the tissue 
without causing injury to the corms. After such treatment the corms 
could be planted in soil known to be free of the pathogenes and be depended 
on to yield a healthy crop. 

Previously to conducting the experiments it was determined that 
the thermal death point of the hard rot and dry rot organisms was about 
50° C. when subjected to this temperature in a test tube culture for 
a period of ten minutes. The tubes were immersed in the hot water as 
soon as new growth appeared from pieces of medium containing mycelium 
which were transferred to the tubes. It was also previously determined 



lyS Bulletin 380 

that conns of from three-fourths inch to one and one-half inches in 
diameter, when subjected to dry heat at 50° C. for one and one-half hours 
or to water at this temperature for one-half hour, were not materially 
harmed. 

Having thus obtained some idea of the relative resistance of both 
corms and the two pathogenes to heat, conns were subjected in 19 13 
to dry heat and to water at 50° C. for one and one-half hours and one-half 
hour, respectively, and the progress of the disease was noted. There 
was enough difference between the length of time required to kill the 
fungi and that which caused no injury to the corms to warrant this treat- 
ment. The corms used were of a single variety and showed considerable 
disease when dug. They were treated on the same day that they were 
harvested. For the hot-water treatment a half-bushel galvanized iron 
measure was used, the heat being supplied by an oil-stove flame, and for 
the dry-air heating a Freas electric oven was used. After treatment 
the corms were cured as quickly as possible and then stored in a cool 
place as usual. Wet weather lengthened the time necessary to thoroughly 
cure the corms more than was desirable. 

In the following January, when the results of this experiment were 
recorded, it was found that seventy per cent of the untreated corms 
bore lesions of either the hard rot or the dry rot disease, while of those 
treated with dry heat and hot water eighty-five and ninety-five per cent, 
respectively, were diseased. In both cases in which treatments were 
given, the corms, besides containing a large percentage of disease, showed 
the lesions to be more advanced than those in the check. Both the 
hard rot and dry rot organisms were isolated from many diseased corms 
of both lots, showing the pathogenes to be still alive. 

In accounting for the increased percentages of disease in the treated 
over the untreated corms, it was found that many of the lesions, besides 
being different in appearance from those produced by the two fungi, 
were identical with those produced on healthy corms which were sub- 
jected to heat under the same conditions and from which neither the 
hard rot nor the dry rot organism could be isolated. These lesions were 
undoubtedly due to injury caused by the heat. However, a sufficiently 
large number of corms bore characteristic lesions of the two diseases, 
and the causal organisms were isolated from enough lesions, to prove that 
the treatments were a failure in kilHng the fungi within the tissue at a 
temperature that would not injure the corm. 

SOIL TREATMENTS 

Experiment i. Chemicals .— Since the organisms causing the hard rot 
and dry rot diseases are able to live over winter in the soil, the possibility 



The Hard Rot Disease of Gladiolus 179 

suggested itself that some chemical might be applied to the soil which, 
either through its toxicity or by its abiHty to change the composition 
of the soil thereby rendering it unsuited for the existence of the pathogenes, 
would serve to eradicate them. Healthy conns could then be planted 
safely in this soil. 

For the experiment in 1912 a plot of land was used on which gladioli 
had been grown for the past three years. The chemicals used and the 
amounts per acre were as follows: air-slaked lime, 1200 pounds; sulfur, 
1000 pounds; air-slaked lime 800 pounds, and sulfur 1000 pounds; sulfate 
of iron, 1800 pounds; acid phosphate, 1200 pounds; acid phosphate, 2100 
pounds. The chemicals were applied by the use of a lime spreader, 
in strips of 10 by 136 feet, a strip of equal width being left between each 
of the treated areas to serve as a check. The entire experiment was 
conducted in triplicate. Across the strips and at right angles to them 
were planted the rows of corms, each row consisting of a single variety. 
During the growing season special care was taken to see that no soil 
was carried from one treated area into another or into the checks. The 
results of the treatments were based on corms removed from a center 
seven-feet strip of each of the treated and the check areas. 

In the following January, when the results of this experiment were 
recorded, it was found that none of the treatments had been of any value. 
No reduction whatever was obtained in the amotmt of disease in treated 
as compared with untreated corms. Since the chemicals were applied 
in as large amounts as is commercially practicable, if not larger, no 
further soil treatments with chemicals have been tried on a large scale. 

Experiment 2. Formalin as a sail disinfectant. — Soil in which seedlings 
had been grown for the past two years was treated in 191 2 with one gallon 
of one-per-cent formalin solution per square foot. The plot was covered 
with heavy burlap for two days after being treated. As soon as the 
odor of formaldehyde could no longer be detected, seeds were planted 
in the treated soil, other seeds being planted in untreated soil to serve 
as a check. 

During the summer the hard rot disease appeared on the foliage of 
these seedlings. No doubt infection occurred from spores blown from 
diseased seedHngs growing near by in untreated soil. The corms were 
harvested in the autumn and stored in a cool room. 

In the following January, when the corms were examined, it was found 
that seventeen per cent of those grown in treated soil were diseased, while 
thirty-seven per cent of the corms from untreated soil showed disease. 
Since the disease appeared on the foliage of these plants during the summer, 
it was impossible to determine whether the source of infection was the 
mycelium of the fungus in the soil, or spores that might have been washed 



i8o Bulletin 380 

down from the leaves to the soil where they would germinate and infect 
the corms. Therefore it was impossible to determine from this experiment 
whether or not the formalin treatment had been of value as a soil dis- 
infectant. The experiment was repeated in 191 5, but no results were 
obtained because the seed planted failed to germinate. 

Experiment j. Formalin as a soil disinfectant. — The value of formalin 
as a soil disinfectant for Septoria Gladioli Passer, and the dry rot fungus 
was further tested by treating soil in which gladioh had been grown for 
the past two years with formalin at the rate of one gallon of one-per-cent 
solution per square foot. Healthy corms were planted in this soil. No 
lesions of the hard rot disease appeared on the foliage during the summer. 
In the following January, when the corms were examined, it was found 
that the treatment had proved of no value in reducing the percentage 
of disease, as compared with healthy corms growing in untreated soil. 
However, the treated plat was not sufficiently isolated from other untreated 
areas to preclude the possibility that infected soil might have been carried 
from untreated soil to that which was treated, and hence the results 
must be considered with that restriction. 

SANITATION 

It has been shown that the hard rot fungus is able to live over winter 
on dead tops left lying about on the ground. It follows that these tops 
should be raked up in the fall and burned. This suggestion appHes 
particularly to the tops of seedlings and cormels, since the disease has 
been observed by the writer to occur on the foHage of but six plants 
of flowering size. It has also been indicated that the fungi causing the 
hard rot and dry rot diseases of gladioh will live in the soil for at least 
four years. Care should therefore be taken that the soil does not become 
infected with the pathogenes. Only healthy corms should be planted 
in soil which it is desired to keep free from these fungi; at least more 
care should be exercised at planting time to see that no corms badly 
diseased are planted. Such corms should be discarded and burned, 
for they will but decay in the soil and infect it with the disease-producing 
organisms. Crop rotation should be practiced. 

BIBLIOGRAPHY 
Allescher, Andreas. Septoria Gladioh Passer. In Kryptogamen- 

Flora von Deutschland, Oesterreich, und der Schweiz [Rabenhorst] 

1:6:789. 1897. 
Childs, J. L. Leaf blight of gladiolus. Florists' ex. 23:541. 1907. 
Crawford, Matthew, and van Fleet, W. The gladiolus, p. 1-98. 191 1. 



The Hard Rot Disease of Gladiolus i8i 

Halsted, Byron D. Fungous diseases of ornamental bulbous plants. 
In Report of the Botanist. New Jersey Agr. Exp. Sta. Rept. 
I4-392-396. 1894. 

Experiments with gladiolus. In Report of the Botanist. New 

Jersey Agr. Exp. Sta. Rept. 17:398-399. 1897. 

Experiments with ornamental plants. In Report of the 



Botanist. New Jersey Agr. Exp. Sta. Rept. 18:334-339. 1898. 
Experiments with ornamental plants. In Report of the 



Botanist. New Jersey Agr. Exp. Sta. Rept. 19:324-327. 1899. 
Experiments with ornamental plants. In Report of' the 



Botanist. New Jersey Agr. Exp. Sta. Rept. 20:408-409. 1900. 
Experiments with ornamental plants. In Report of the 



Botanist. New Jersey Agr. Exp. Sta. Rept. 21:461-462. 1901. 
Hendrickson, I. S. Gladioli. American Glad. Soc. Bui. 3:5-13. 1911. 
Hicks, D. C. Notes upon the gladiolus and its culture. Vermont State 

Hort. Soc. Rept. 4:32-36. (Part of the 27th Ann. Rept. Vermont 

Stat- Bd. Agr.) 1907. 
Pax, F. Ixioideae-Gladioleae. /;/ Die natiirlichen Pflanzenfamilien 

[Engler und Prantl] 2:5:153-154. 1889. 
Prillieux, E. E., and Delacroix, G. Pathologic vegetale. Maladies 

bacillaires de divers vegetaux. Acad. Sci. Paris. Compt. rend. 

118:668-671. 1894. 
Robinson, W. Gladiolus. In The English flower garden and home 

grounds, p. 575-578. 1883. 
Saccardo, p. a. Septoria Gladioli Passer, /n Sylloge fungorum 3 : 574. 

1884. 
Wallace, Errett. Some bulb rots of gladioli. Thesis for degree of 

M. S. in Agr., Cornell University, 1909. (Unpublished.) 

Diseases of gladioli. Rural New-Yorker 69:355. 19 10 (a). 

Gladiolus bulb rots. Cooperative experiments. Gardening 

18:308. 1910 (b). 



